In a circular saw, for example, in order to increase cutting efficiency, it is necessary to increase the rotation speed of a saw blade during cutting. To this end, it is necessary to increase the rotation speed during no-load. Even at the markets, in order to emphasize a smooth cutting performance, the manufactures tend to appeal the high-speed rotation during no-load.
If the rotation speed during no-load increases, there are problems that vibration and noise increase and power consumption unnecessarily increases. These problems are not limited to a circular saw, but are common to other electric power tools such as a grinder.